1. Field of the Invention
This invention relates generally to towers for drilling machines, and controlling the tilt thereof.
2. Description of the Related Art
There are many different types of drilling machines for drilling through a formation. Some of these drilling machines are mobile and others are stationary. Some examples of mobile and stationary drilling machines are disclosed in U.S. Pat. Nos. 820,992, 3,195,695, 3,245,180, 3,561,616, 3,692,123, 3,695,363, 3,708,024, 3,778,940, 3,805,902, 3,815,690, 3,833,072, 3,905,168, 3,968,845, 3,992,831, 4,016,687, 4,020,909, 4,595,065, 4,606,155, 4,616,454, 5,988,299, 6,527,063, 6,672,410, 6,675,915, 7,325,634, 7,347,285 and 7,413,036, as well as in U.S. Patent Application No. 20080210469. Some drilling machines, such as the one disclosed in U.S. Pat. No. 4,295,758, are designed to float and are useful for ocean drilling. The contents of these cited U.S. patents and the patent application are incorporated by reference as though fully set forth herein.
A typical mobile drilling machine includes a vehicle and tower, wherein the tower carries a rotary head and drill string. In operation, the drill string is driven into the formation by the rotary head. In this way, the drilling machine drills through the formation. More information about drilling machines, and how they operate, can be found in the above-identified references.
In some situations, it is desirable to drill at an angle. Drilling at an angle is useful so that more regions of a formation can be reached with the drill string. For example, in some situations, the drilling machine cannot be positioned directly over a desired region of the formation, so it is not possible to drill straight down and reach this region of the formation. Hence, angled drilling is useful so that the drilling machine can reach a desired region of a formation without being directly over it. In this way, there are many more options available when selecting the location to position the drilling machine.
Angled drilling is typically accomplished by tilting the tower relative to an axis of the drilling machine so that the drill string is tilted in response. More information regarding tilting a tower is provided in U.S. Pat. Nos. 3,245,180, 3,561,616, 3,815,690, 3,778,940, 3,905,168, and 3,992,831, and U.S. Patent Application No. 20080210469, as well as some of the other references mentioned above. However, it is desirable to better control the angle that the tower is tilted, and to provide more stability to the tower when it is in a tilted condition.